1. Field of the Invention
The present invention relates to a structure of a combustion chamber for an in-cylinder fuel injection engine in which fuel is injected directly into the cylinder.
2. Background art
Generally, since the stratified charge combustion strategy provides a readily ignitable rich air-fuel mixture in the vicinity of the spark plug with the overall air-fuel ratio retained in the lean condition, the engine employing the stratified charge combustion strategy has an excellent fuel economy performance.
An engine 1 shown in FIG. 8 is an example of an in-cylinder fuel injection two cycle engine intended to realize the stratified charge combustion according to the prior art. The engine 1 comprises a cylinder block 3 having a cylinder 2, a piston 4 reciprocating in the cylinder 2 and a cylinder head 5. A combustion chamber is formed by the cylinder 1, the top surface of the piston 4 and the cylinder head 5.
A cavity 4a is formed on the top surface of the piston 4, a fuel injector 6 is disposed approximately coaxially with the center line CL of the cylinder bore, and a spark plug 7 is disposed slightly diagonally in the vicinity of the fuel injector 6.
There are provided a booster port 2a, a scavenging port 2b and an exhaust port 2c on the wall surface of the cylinder 2 and these ports are opened and closed respectively by the reciprocating motion of the piston 4. The booster port 2a and the scavenging port 2b are ports for introducing a fresh air including lubrication oil into the cylinder 2. The exhaust port 2c is a passage for discharging exhaust gas therethrough and it is provided opposite to the booster port 2a. 
In this type of the combustion chamber, the spark plug 7 ignites the rear end of the fuel spray in a first stage diffusion. The fuel spray in the first stage diffusion is a fuel at a stage of diffusing and not reaching the top surface of the rising piston 4.
As described before, according to this prior art, the fuel injector 6 is close to the spark plug 7, so that the rear end of the sprayed fuel is ignited by the spark plug 7 before the sprayed fuel collides with the top surface of the rising piston 4. This disposition of the spark plug 7 adjacent to the fuel injector 6 incurs a temperature-rise of the fuel injector 6 itself, this causing the malfunction of the fuel injector 6, an increase of carbon deposits and the like.
Further, the ignition of the fuel spray in the first stage diffusion tends to provide an inadequate atomization in the sprayed fuel and this inadequate atomization causes a wetting in the spark plug 7, this often leading to a spark plug fouling. Further, supposing a case of the ignition of the fuel spray in a second stage diffusion, that is, a state of the fuel spray after a collision against the piston 4, since the flow of scavenging acts as carrying the fuel spray away from the spark plug 7, this strategy of combustion makes it difficult to realize the stratified charge combustion.
It is an object of the present invention to provide a combustion chamber structure of an in-cylinder direct fuel injection engine capable of realizing the stratified charge combustion and it is a further object of the present invention to provide an internal combustion engine free from serious malfunctions like misfires.